Photo-electric densitometer

ABSTRACT

An improved portable type of photo-electric densitometer, which contains a photometer section as well as display means within its main body, and in which one of the legs of the main body is provided with a light inlet opening which functions, when said densitometer is placed on a sheet carrying an image thereon, as an optical path for leading the light transmitted through the sheet portion beneath said particular one leg to a photo-electric element in said photometer section to give a direct reading of the image density at said sheet portion on said display means.

United States Patent 1191 Abe June 4, 1974 PHOTO-ELECTRIC DENSITOMETER OTHER PUBUCATIONS [75] inventor? Toshio Tokyo Japan Joscheck; Lichtelektrischer Reflexionsmesser. Sie- [73] Assigneez Konishimku photo Industry CO mens Zeitschrift Mai/Jun! 1933, pages 1 10-1 1.?

Ltd., Tokyo, Japan Primar E.\'aminerRonald L. Wibcrt [22] Flled: July 1972 Assistant EmminerF. L. Evans 2 App] 2 9559 Attorney, Agent, or FirmBierman & Bierman Related US. Application Data I 57] ABQTRACT [63] Continuation of Ser. No, l()l.065, Doc. 23. I970, i

abandoned. An improved portable type of photo-electric densitometer, which contains a photometer section as well 521 US. Cl 356/202, 356/209, 356/212 as display mehhs withih its hihih body, in which 51 Int. Cl. 001" 21/48 hhe of of the main body is Provided with a 58 Field of Search 356/201-206 light ihiei opehihg which functions when Said dehsi 356/209 2li tometer is placed on a sheet carrying an image thereon, an optical path for leading the light trans- [56] References Cited mitted through the sheet portion beneath said particular one leg to a photo-electric element in said photom- UNITED STATES PATENTS eter section to give a direct reading of the image density at said sheet portion on said display means. oo t 1 1 3,535,046 10/1970 Denner 356/212 1 Claim, 4 Drawing Figures 1 PHOTO-ELECTRIC DENSITOMETER This is a continuation of application Ser. No. 101,065,'filed Dec. 23, 1970, now abandoned, which is based on Japanese application Ser. No. 123847/1969, filed Dec. 29, I969.

The present invention relates to a portable type of photo-electric densitometer for measuring a density of black-and-white pictures by transmission.

The densitometers in the prior art had disadvantages that the body of the instrument was large and that upon densitometry complex operations were required.

The present invention has it as an object to provide a portable type of photo-electric densitometer, which is compact in size and simple in operation, in view of the aforementioned disadvantages in the prior art.

The densitometer according to the present invention also has an advantage that since one of the legs is utilized as a light inlet path for the photometer section, a tight contact between the boundary wall of the light inlet path and the sheet to be measured is assured and thus no external light can invade into the light inlet path.

In addition, the present invention affords another advantage that the scale of the display means is graduated substantially at equal intervals to give a direct reading of the density value.

Now the present invention will be described with reference to its preferred embodiment illustrated in the accompanying drawings, wherein:

FIG. 1 is a perspective view of one preferred embodiment of the present invention,

FIG. 2 is a cross-section view of the same embodiment in FIG. 1,

FIG. 3 is an enlarged view of a light receiver section in the same embodiment, and

FIG. 4 is a circuit diagram of the same embodiment.

Referring now to the drawings, the instrument body I is provided with a meter 2 including a density scale 20, a zero adjust knob 3 of the meter 2, and legs 4 and 5, 5 The leg 4 also serves as a photometer section as described later.

In the followings, the respective sections of this photo-electric densitometer will be described for each item:

PHOTOMETER SECTION:

The leg 4 is provided with a light inlet opening 10. Above the light inlet opening are disposed a slide plate 11 having an aperture slit l3 and a light receiver section 12 consisting of a photo-electric element such as, for example, a cadmium sulfide element.

ZERO ADJUST MECHANISM FOR METER:

The zero adjust knob 3 is pivotably mounted on the body 1, and is provided with an elongated opening 14.

. the zero adjust knob 3 while watching the meter 2.

ELECTRIC CIRCUIT:

In FIG. 4, reference P indicates a photo-electric element as of cadmium sulfide which forms the light receiver section 12 as in FIG. 2, reference E indicates power supply to terminals, reference S indicates a switch, FT, and FT indicate field effect transistors, respectively, T and T indicate amplifier transistors, T indicates a power supply stablizing transistor, M indicates a meter corresponding to the meter 2 in FIG. I, and D D and D indicate diodes, respectively. Reference R indicates a resistor connected in parallel to the photo-electric element P, and it is provided for the purpose of flowing a certain amount of electric current through a network I even if the amount of incident light to the photo-electric element F is small and thus said element shows a high resistance, to apply a voltage to the gate of the field effect transistor FT Reference R indicates a resistor having substantially the same resistance as the resistorR Reference D, indicates a non-linear element such as a diode, which is an element for producing a voltage varying logarithmically with respect to the change of the electric current flowing through said element. Reference D,-, is also a non-linear element having the same function as element D The resistor R non-linear element D field effect transistor FT 2 and transistor T form a reference network in contrast to the photometric network consisting of the photo-electric element F, resistor R non-linear element D field effect transistor FT, and transistor T,.

When a light is projected to the photo-electric element P under the state of closing the switch S, an electriccurrent substantially in proportion to the amount of incident light flows through the non-linear element D and due to this electric current a voltage proportional to the logarithm of this current value is produced across the non-linear element'D That is, since the gate of the field effect transistor FT, is applied with a potential proportional to the logarithm of the intensity of incident light, an electric current proportional to the logarithm of the intensity of incident light flows through the output circuit of the field effect transistor FT On the other hand, through the meter M flows a difference current between the current from the aforementioned reference network and the above mentioned photometric network. Therefore, the value indicated by the meter M is the logarithm of the intensity of incident light to the photo-conductive element P. In case that the incident light to the photoconductive element P is the light transmitted through a light transparent sheet, then the value indicated by the meter directly represents the image density, and obviously the scale of the meter M is graduated substantially at equal intervals.

Now the operation of this photo-electric densitometer will be described. At first, the instrument body is placed on a transparent glass plate (in the case of a parallel light photographic densitometry) or on a light scattering plate (in the case of a scattered light densitometry), the switch S is closed (the switch S is preferably closed by the actuation of the zero adjust knob 3), the zero adjust knob 3 is turned, the slide plate 11 is made to slide to adjust the amount of incident light to the light receiver section 12, and the pointer of the meter is preset at the zero point. Subsequently. a transparent sheet is placed on the transparent plate or the light scattering plate, then the instrument body 1 is placed on said transparent sheet while registering the leg 4 with the portion of the sheet whose density is to be measured, and the value indicated by the meter is read out.

In summary, according to the present invention. owing to the fact that the photo-electric densitometer is formed in an overplace type and utilizes its one leg as a part of the photometer section, only by placing the photo-electric densitometer on the transparent sheet to be measured, a harmful light can be entirely shut out and also the image density can be measured while invention has practically excellent features that theinstrument body is made extremely compact. and that a density indication which is easy to be read out and accurate, can be obtained.

What is claimed is:

l. A photoelectric densitometer for placement on a sheet carrying an image thereon for measuring its density and which utilizes a light source, said photoelectric densitometer comprising at least three legs for steadying said densitometer, and a photometer section, at least one of said legs having a single opening therein for permitting light to enter said one leg said one leg being positioned on said sheet to prevent stray light from entering the densitometer, said one leg serving also as a part of the photometer section, said photometer section comprising a photoelectric element having an output responsive to the light falling thereon and being mounted so as to receive the light entering through said one leg, amplifier means for logarithmically converting and amplifying the output response signal from said photoelectric element, a meter connected to the output circuit of said amplifier means and having a uniform image density scale, zero point adjust means for said meter, and compensating circuitry for obtaining a difference signal between the logarithmically converted output signal and a reference signal. 

1. A photoelectric densitometer for placement on a sheet carrying an image thereon for measuring its density and which utilizes a light source, said photoelectric densitometer comprising at least three legs for steadying said densitometer, and a photometer section, at least one of said legs having a single opening therein for permitting light to enter said one leg said one leg being positioned on said sheet to prevent stray light from entering the densitometer, said one leg serving also as a part of the photometer section, said photometer section comprising a photoelectric element having an output responsive to the light falling thereon and being mounted so as to receive the light entering through said one leg, amplifier means for logarithmically converting and amplifying the output response signal from said photoelectric element, a meter connected to the output circuit of said amplifier means and having a uniform image density scale, zero point adjust means for said meter, and compensating circuitry for obtaining a difference signal between the logarithmically converted output signal and a reference signal. 